In general, knifes become blunt after being used, and a grinding stone is usually used to sharpened the knives. Conventional grinding stones are heavy and not easy to store, and when in use, the user has to hold the grinding stone, so the chance to injure the user is high. Also, when during the grinding process, the user has to adjust the grinding angle to achieve a better result. Therefore, there remains a need for a new and improved knife sharpener to overcome the problems stated above.